1. Field of the Invention
This invention relates to a therapeutic system, in the form of an ocular insert, and to a method for treating aqueous deficient dry eye.
2. Description of the Prior Art
The term "dry eyes" is used to denote a multitude of ophthalmic conditions that manifest themselves in common symptoms ranging from slight irritation to incapacitating discomfort and blindness from corneal damage. These conditions have been divided by causation into two categories: those caused by aqueous deficiency, both congenital and acquired, and those caused by mucin deficiency. The aqueous deficient dry eye is characterized by insufficient aqueous tear production to maintain a stable tear film; whereas the mucin deficient eye is characterized by instability of the tear film despite adequate aqueous tear production. The present invention relates to the aqueous deficient dry eye.
New Concepts In Ocular Xerosis, Dohlman, C. H., Trans. Ophthal. Soc. U.K. 91, 105-117 (1971), and Tear Substitutes in the Treatment of Dry Eyes, Lemp. M. A. Int. Ophthal. Clin. 13, 145-153 (1973) give excellent reviews of the available therapy for treating aqueous deficient dry eyes. As reported by Lemp, the treatment of aqueous deficient dry eyes has been limited primarily to using artificial tears to periodically supplement inadequate production of tears. Isotonic saline drops were used initially as artificial tears but were found to provide only short-lived relief. Also, they have to be instilled on the order of three to twelve times a day depending upon the severity of the condition. In order to prolong relief, water soluble polymers have been added to the isotonic saline solution to make it more viscous. In this regard, artificial tear solutions containing methyl cellulose, methyl cellulose derivatives, ethyl cellulose, polyvinyl alcohol and/or other soluble polymers are commercially available. However, it is reported that even these more viscous solutions provide only short-lived relief and do not remain in contact with the cornea for longer than 15 minutes after instillation.
Hydrophilic ("soft") contact lenses used in conjunction with artificial tears have been used to treat aqueous deficient dry eyes. However, such treatment has been experimental and also requires frequent instillation of artificial tear solution. Dohlman, supra, has also suggested that constant rate delivery of small amounts of fluid would be more desirable than using artificial tear drops in the case of severe cases of aqueous deficient eyes. Specifically, he describes a system that delivers 1-3 ml/hr of solution to the eye on a continuous basis involving a small pump that is connected to tubing that in turn is attached to spectacle frames and extends into the sac of the eye.
Potential Use of Ocular-Insert Therapy in Dry Eyes, Pavan-Langston, D., Int. Ophthal. Clin. 13, 231-238 (1973) discusses the potential use of ocular inserts to treat dry eyes. It concludes that ocular inserts are not good candidates for treating aqueous deficient dry eyes, but that they might be used to treat mucin deficient dry eyes.